Which when they had taken up - When they had raised up the boat into the ship, so as to secure it.
They used helps - They used ropes, cables, stays, or chains, for the purpose of securing the ship. The danger was that the ship would be destroyed, and they therefore made use of such aids as would prevent its loss.
Undergirding the ship - The ancients were accustomed to pass cables or strong ropes around a vessel to keep the planks from springing or starting by the action of the sea. This is now called “frapping” a vessel. The operation of “frapping” a vessel is thus described in Falconer’s Marine Dictionary. “To frap a ship is to pass four or five turns of a large cable-laid rope round the hull or frame of a ship to support her in a great storm, or otherwise, when it is apprehended that she is not strong enough to resist the violent efforts of the sea.” An instance of this kind is mentioned in Lord Anson’s voyage round the world. Speaking of a Spanish man-of-war in a storm, he says, “They were obliged to throw overboard all their upper-deck guns, and take six turns of the cable round the ship to prevent her opening.”
Lest they should fall into the quicksands - There were two celebrated syrtes, or quicksands, on the coast of Africa, called the greater and lesser. They were vast beds of sand driven up by the sea, and constantly shifting their position, so that it could not be known certainly where the danger was. As they were constantly changing their position, they could not be accurately laid down in a chart. The sailors were afraid, therefore, that they should be driven on one of those banks of sand, and thus be lost.
Strake sail - Or, rather, lowered or took down the mast, or the yards to which the sails were attached. There has been a great variety of interpretations proposed on this passage. The most probable is that they took down the mast, by cutting or otherwise, as is now done in storms at sea, to save the ship. They were at the mercy of the wind and waves, and their only hope was by taking away their sails.
And so were driven - By the wind and waves. The ship was unmanageable, and they suffered it to be driven before the wind.